In the casting, particularly the continuous casting, of a liquid in the liquid state from an upper metallurgical vessel toward a lower vessel, it is necessary to ensure a certain level of control on the metal flow and in particular on the casting flow rate. Various means used to this end are known: internal means such as a stopper or external means such as the slide gate valve (linear or rotary).
Most slide gate valves comprise a set of refractory plates, each provided with at least one pouring orifice, inserted in a device permitting a relative displacement of the plates while ensuring their compression so that the metal stream could more or less easily flow through the orifices of adjacent plates depending on the throttling rate of the orifices. In the known devices, the relative displacement of the plates (at least one of them being mobile and at least one being fixed or stationary) is carried out according to a linear, rotary or any other trajectory translation move. The relative displacement of the plates is generally ensured by the force exerted by a cylinder (hydraulic, pneumatic or electromechanical) or even by a motorized driving device. Throughout the casting, the throttling rate of the plates is continuously adjusted so as to maintain the casting conditions (flow rate, metal level in the upper vessel, etc.) in suitable limits.
Such slide gate valves can be operated for casting from a furnace towards a ladle or a converter, from a converter toward a ladle or from a ladle toward a tundish. The present invention relates to these different possibilities. For the sake of conciseness, it will however mainly be described in the context of casting from a ladle toward a tundish.
During the casting operations, the refractory plates are subjected to many severe stresses which, in the long run, are responsible for their wear. In particular, these are thermal (high casting temperature), chemical (composition of the cast metal, of the slag), mechanical (level of the throttling, number of relative displacements, etc.), thermo-mechanical (thermal shock), etc. stresses. Further, certain events or incidents occurring during the casting operation might have a significant impact on the state of the refractory plates. For example, in the case of non-natural opening of the upper vessel or in the case of clogging of the orifice during the casting, it might be necessary to use a torch or other thermal rods in order to clear the pouring orifice of the plate. Such recourse to a torch is obviously disastrous as to the state of the plate. All these stresses generate radial wear of the pouring orifice, an erosion of the throttling lips (portion of the orifice periphery used to perform the throttling of the liquid metal stream), cracks of all kinds, more or less important disintegration or melting of the refractory material or even the penetration of foreign bodies inside the refractory material.
These last years, the quality of the refractory materials used for the manufacture of such plates as well as the optimization of their shape has permitted a considerable increase in their life time so that after a first use in a slide gate valve during the casting from an upper vessel towards a lower vessel, it is actually possible to reuse these plates a certain number of occurrences.
After each use of a refractory plates set, it is therefore necessary to decide whether these plates can be reused or must be discarded. The method generally practiced in the metallurgical industry consists in performing a visual inspection of the refractory plates, the decision resting essentially on the appearance of the plates. This visual inspection is performed at the level of the so-called “maintenance” zone (for the metallurgical vessels) where the metallurgical vessels are laid down so as to permit an easy access to the slide gate valve. It will be noted that this preparation zone is often far remote from the casting zone where the actual casting operations are performed so that, practically very little information is exchanged between the operators of these different zones.
The conditions of performing the visual inspection of the plates are far from being optimal. The plates are indeed only visible through the pouring orifice; therefore, this does not allow the inspection of the state of the sliding surfaces where the degradations are the most important. In most of the cases, the partial dismantling of the gate on this occasion is prohibited since it generates an over-consumption of manpower and a significant loss of time and especially since such a dismantling generates a very significant thermal shock at the level of the plates.
The visual inspection of the plates is therefore performed by an operator having a certain expertise in this particular field, since his decision as to the possible reuse or rejection of a refractory plate is crucial. The reuse of a deteriorated plate can indeed cause a very serious accident (breakage) which can compromise the safety of the operators or, at least, very seriously damage the casting installation. On the other hand, the premature rejection of a plate causes significant economic (increase of the reduction costs) and environmental damages. This decision is very subjective and depends largely upon the experience and the skill of the operator.
JP-A-2003181625 describes a method of measure of the wear level of the plates of a slide gate valve used to control the flow of a molten metal. The wear level is determined with the help of a specific tool. An end of the tool is connected to the casting orifice of the plate for a direct measure. Each new plate must be equipped with such a tool.